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We asked how she felt when she was away from the wind turbines, to which she replied:
“I did manage to take a vacation towards the end of August and for the two weeks we were away I was perfectly fine.”
The goal of our work in this field is to understand whether the physiology of the ear can, or cannot, explain the symp- toms people attribute to wind turbine noise. As it is generally the case when debate influences a specific industry’s financial interests and legal well-being, the scientific objectivity of those associated with the industry can be questioned. Liabil- ity, damage claims, and large amounts of money can hang in the balance of results from empirical studies. Whether it is
a chemical industry blamed for contaminating groundwater with cancer-causing dioxin, the tobacco industry accused of contributing to lung cancer, or athletes of the National Foot- ball League (NFL) putatively being susceptible to brain dam- age, it can be extremely difficult to establish the truth when some have an agenda to protect the status quo. It is only when sufficient scientific evidence is compiled by those not working for the industry that the issue is considered seriously.
Origins of Our Involvement
in Infrasound from Wind Turbines
What is the evidence leading us to conclude that unheard infrasounds are part of the wind turbine problem, and how did we become involved in this debate? We are small group of basic and applied scientists, which means that our work addresses fundamental questions on how the ear works in normal and diseased states. While developing paradigms
for our studies, we had been using a classic technique called “low-frequency biasing” – measurement of auditory responses to a test sound within the range of audibility, while simulta- neously presenting a low-frequency tone (e.g., 4.8 to 50 Hz) to displace the sensory organ of the inner ear. Some auditory responses saturate when displaced by the bias tone, which can be used to establish whether the sensory organ is vibrating symmetrically or whether a fluid disturbance has displaced
it to one side. A condition called “endolymphatic hydrops,”
“Almost all measurements of wind turbine noise are A-weighted, making the unjustified assumption that hearing is the only way by which infrasound generates physiologic effects.”
which is found in humans with Ménière’s disease, can displace the sensory organ as the space containing the fluid called endolymph swells. In our animal experiments we initially used 20 to 50 Hz bias tones, but for many reasons, and in large part based on a study in which we found that the ear responded down to 1 Hz (Salt and DeMott, 1999), we started using the lowest frequency our hardware could generate, 4.8 Hz, a frequency considered to be infrasound. Over the course of hundreds of experiments, we have found numerous biasing effects with 4.8 Hz tones at levels of 80 to 90 dB SPL (i.e., -13 to -3 dBA). We also found that the ear became about
20 dB more sensitive to infrasonic bias tones when the fluid spaces in the cochlear apex were partially occluded, as occurs with endolymphatic hydrops.
In late 2009, the first author received a report of a woman with Ménière’s disease whose symptoms – primarily dizziness and nausea – were severely exacerbated when she was in the vicinity of wind turbines. From our animal data, we knew this woman was likely hypersensitive to very low-frequency sounds. Our subsequent review of the literature on wind-tur- bine noise revealed two aspects that were absolutely astound- ing:
1. Almost all measurements of wind turbine noise are A- weighted, making the unjustified assumption that hearing
is the only way by which infrasound generates physiologic effects. The few studies that reported un-weighted measure- ments of wind-turbine noise, or recalculated spectra by re- moving the A-weighting from published A-weighted spectra, clearly demonstrated increasing energy towards low frequen- cies with highest energy levels in the infrasound region. We were surprised that objective full-frequency measurements showed that wind turbines generate infrasound at levels capable of stimulating the ear in various ways. Under such circumstances, A-weighting measurements of turbine noise would be highly misleading.
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